The present invention relates to a wastewater screening device for retaining solids at overflows which are carried along in the wastewater, having an apparatus for clearing away the screenings. The wastewater screening device includes a drive for the screen clearing apparatus which is upstream of an associated overfall, and is oriented such that the wastewater flows through the screening device from bottom to top.
Wastewater screening devices are generally know from DE 42 15 002 A1. In the latter, the screening device has a plurality of rods which are arranged in a parallel relationship, with a space or distance between the rods of several millimeters. An apparatus for clearing away the screenings lodged between the screening rods has wiper elements, which are moved by a drive that is arranged between the screening rods, and can be moved to and fro in order to remove the screenings from between the screening rods. The rods of the screening system are of a straight design, and arranged horizontally. The wiper elements are mounted in pivoting levers, which can pivot about an axle arranged above the rods. The rods are pivoted by a drive unit, which is mounted in an upper cross member of a frame of the screening device, and which is composed of a motor and a gear mechanism, with the drive unit being attached to a cover or to a wall of a structure which forms the rain overflow basin. It contemplates using an electric, pneumatic or hydraulic cylinder as the linear drive.
A disadvantage associated with this type of screening device is that the structure for holding the screening device, which includes the apparatus for clearing way the screenings and the drive, is extremely tall owing to the arrangement of the drive above the maximum wastewater level. Furthermore, the positioning of the screening device, and in particular of the drive, is tied to a predetermined location, because the drive requires a power source for the motor, such as an electric motor, a pneumatic motor, or a hydraulic cylinder. It is therefore not possible to mount the screening device at any desired location. On the other hand, this outside or extraneous energy drive is located in a region of the installation, such as a high water spillway installation, in which it is subjected to moisture, which results in an increased risk of faults or of failure of the drive for the screen clearing apparatus.
EP 1 223 252 A2 describes a screen device which is mounted in a dividing wall between a wastewater main channel and an associated side channel. This screening device has a fixed drum which is enclosed at the sides, and divides the main channel from the side channel. The drum is provided with a large opening on its side facing the main channel, with the result being that the wastewater can pass into the drum from the main channel via the opening. On the side facing the side channel, the drum is provided in its lower region with a screen, so that material which is carried along in the wastewater is retained at the drum when the flow passes through the drum, and only clean water can pass from the drum into the side channel. An apparatus for clearing away the material is rotatably mounted within the drum. The device is driven by a waterwheel, which is arranged downstream of the screen in the direction of flow. The rotating waterwheel rotates the apparatus for clearing away the screenings via a belt or a drive.
Screening devices which are configured in a similar manner to that disclosed in DE 42 15 002 A1 are also described, for example, in DE 195 15 924 A1, WO 98/31882, WO 99/49145 and WO 01/75249 A1.